Button cells normally have a housing comprising a housing cup (often also referred to as a housing pan) and a cell cover. By way of example, the cell cup and the cell cover may be produced from nickel-plated deep-drawn metal sheet as a stamped drawn part. Usually the cell cup is of positive polarity and the cell cover is of negative polarity. The housing may contain widely different electrochemical systems, for example, zinc/MnO2, primary or secondary lithium-systems or secondary systems like nickel/cadmium or nickel/metal hydride.
Button cells are normally closed in a liquid-tight manner by flanging the edge of the cell cup around the edge area of the cell cover in conjunction with a plastic ring arranged between the cell cup and the cell cover and at the same time acts as a sealing element as well as providing isolation between the cell cup and the cell cover. By way of example, such button cells are disclosed in DE 31 13 309.
DE 196 47 593 describes button cells in which the plastic ring is replaced by a sealing element produced by thermoforming from a film. Compared to classical seals produced by injection molding, the described film seals have the advantage that they can be produced having a comparatively low thickness and therefore a relatively small volume. Film seals make it possible to produce button cells having notably improved capacity.
All these button cells have in common that during their assembly problems may arise as a result of comparatively low thicknesses of the walls of the cell cup and the cell cover as this may lead to deformations when a mechanical load is applied. Critical are in particular loads applied during the flanging process. The goal of the flanging is to provide a form-fitting connection between the cell cup and the cell cover. During the flanging the cut edge of the cell cup is bent radially inward over the edge of the cell cover. The seal between the cell cup and the cell cover is thereby compressed. During this process axial loads arise which may lead to deformation or even breakdown of the base of the cell cup and the cell cover. As long as the mechanical load on the cup and the cover is not distributed evenly, damage of the cell cup and/or the cell cover can occur and, as a consequence, leaks may result.
It could therefore be helpful to provide a technical solution which does not suffer from such problems. In particular, it could be helpful to provide a new method for producing button cells, wherein the housing parts to be assembled are exposed to mechanical loads in the axial direction as low as possible. Thus, the button cells should be produced by a construction as simple as possible and, simultaneously, by good leak-tightness properties and a high capacity.